1. Field of the Invention
The present invention relates to a tape guide post mechanism for use in a magnetic recording/reproducing apparatus, such as a videotape recorder (VTR).
2. Description of the Related Art
In recent years, there has been a growing demand for decreases in size and price of magnetic recording/reproduction apparatus, such as VTRs, camcorders, etc.
Hereinafter, a tape guide post mechanism for use in a conventional magnetic recording/reproducing apparatus is described.
FIG. 6 is a plan view of a magnetic recording/reproducing apparatus which uses a conventional tape guide post mechanism. FIG. 6 shows that a tape 2 has been pulled out from a cassette 1 by tape guide posts 8, 9, 10, and 13, and looped around a rotatable head cylinder 6. In this state, recording/reproduction of data or information to/from the tape 2 can be performed. In FIG. 6, some parts are omitted (i.e., not shown) for clarity of illustration.
As shown in FIG. 6, reference numeral 2 denotes a tape, which is wound around an S-reel 4a and a T-reel 5a stored in the cassette 1. For clarity of illustration, the external shape of the cassette 1 is represented by a dashed line. Reference numeral 3 denotes a base of the magnetic recording/reproducing apparatus, on which the cassette 1 is mounted. Reference numeral 4 denotes an S-reel bed, which is rotatably and axially supported on the base 3. The S-reel bed 4 is engaged, and rotates integrally, with the S-reel 4a. 
Reference numeral 5 denotes a T-reel bed, which is rotatably and axially supported on the base 3. The T-reel bed 5 is engaged, and rotates integrally, with the T-reel 5a. Reference numeral 15 denotes a tension arm (post arm). The tension arm 15 has: a tension post 8, which is one of the tape guide posts, and which is one of the constituent elements of a tape running system; and a hole 15a. The base 3 has a tension arm shaft 14, which is provided so as to penetrate through the hole 15a, so that the tension arm shaft 14 rotatably supports the tension arm 15. Reference numeral 18 denotes a tension band, one end of which is supported by a shaft 15b formed in the tension arm 15, and the other end which is fixed to the base 3 with a band fixture screw 19. The intermediate portion of the tension band 18 is wound around a cylindrical portion 20 of the S-reel bed 4. The tension arm 15 is urged by an urging spring 15c around the tension arm shaft 14 in a counterclockwise direction.
Reference numeral 6 denotes a rotatable head cylinder provided on the base 3. The rotatable head cylinder 6 has a rotatable magnetic head, through which a signal is recorded in/reproduced from the tape 2 that is looped around the rotatable head cylinder 6. Reference numeral 7 denotes a S1-post, which is one of the tape guide posts. Reference numeral 11 denotes a T2-post, which is one of the tape guide posts. The S1-post 7 and the T2-post 11 are fixed to the base 3, and are constituent elements of the tape running system. Reference numeral 9 denotes a S2-post, which is one of the tape guide posts. Reference numeral 10 denotes a T1-post, which is one of the tape guide posts. The S2-post 9 and the T1-post 10 are constituent elements of the tape running system. Reference numeral 12 denotes a capstan shaft, and reference numeral 100 denotes a pinch roller. The tape 2 which is sandwiched by the capstan shaft 12 and the pinch roller 100 is driven in a forward/reverse direction by forward/reverse rotation of the capstan shaft 12. Reference numeral 13 denotes a T3-post, which is one of the tape guide posts, and is a constituent element of the tape running system. The T3-post 13 is formed in a T3-arm 17 which is a post arm. The T3-arm 17 has a hole 17a. A T3-arm shaft 23a which is formed on the base 3 is provided so as to penetrate through the hole 17a, so that the T3-arm shaft 23a rotatably supports the T3-arm 17. FIG. 6 shows that the tape 2 has been pulled out of the cassette 1 by the tension post 8, the S2-post 9, the T1-post 10, and the T3-post 13.
The tape running system shown in FIG. 6 is now described. The tape 2 pulled out from the S-reel 4a is first looped around the S1-post 7 on the base 3, and then, looped around the tension post 8 and the S2-post 9. Further, the tape 2 is looped around the rotatable head cylinder 6, and around the T1-posts 10 and the T2-posts 11. Thereafter, the tape 2 is looped around the capstan shaft 12 and the T3-post 13. Thereafter, the tape 2 is wound around the T-reel 5a. 
Hereinafter, an operation of the tape guide post mechanism of the conventional magnetic recording/reproducing apparatus having the above described structure is described with reference to FIGS. 7 through 9.
FIG. 7 is a cross-sectional view showing the T3-arm 17 of the conventional tape guide post mechanism. FIG. 8 is a cross-sectional view showing the state of the T3-arm 17 when a tape tension is applied to the T3-arm 17. FIG. 9 is a perspective view showing the details about engagement between the hole 17a of the T3-arm 17 and the T3-arm shaft 23a. 
In FIG. 7, the tape 2 is not looped around the T3-post 13. The hole 17a of the T3-arm 17 is rotatably engaged with the T3-arm shaft 23a formed on the base 3. The T3-arm 17 is prevented by a stoppage ring 21 from being upwardly disengaged from the T3-arm shaft 23a. Further, some space 22 is necessarily provided between the internal wall surface of the hole 17a and the external side surface of the T3-arm shaft 23a such that the T3-arm 17 is rotatable around the T3-arm shaft 23a. 
When the tape 2 is looped around the T3-post 13 so as to have a predetermined contact area therebetween which corresponds to a predetermined angular distance around the T3-post 13 so that the tape 2 can run, tape tension Ta is applied to the T3-post 13 as shown in FIG. 8. Due to tape tension Ta, a rotation moment is caused in the T3-arm 17 and the T3-post 13 in the direction of arrow M. Accordingly, the T3-arm 17 slightly rotates in the direction of arrow M as shown in FIG. 8. As a result, the internal wall surface of the hole 17a of the T3-arm 17 is in contact with the external side surface of the T3-arm shaft 23a at an upper contact point 30 and a lower contact point 31 as shown in FIGS. 8 and 9.
FIG. 9 shows the slanted T3-arm 17 only in the vicinity of the T3-arm shaft 23a. As seen from FIG. 9, a hole center line 33 between the center of the upper opening of the hole 17a of the T3-arm 17 (xe2x80x9cupper hole center 32axe2x80x9d) and the center of the lower opening of the hole 17a of the T3-arm 17 (xe2x80x9clower hole center 32bxe2x80x9d) is slanted with respect to the longitudinal axis of the T3-arm shaft 23a. 
However, the above conventional structure involves some problems as described below with reference to FIGS. 8 and 9.
Since the T3-post 13 is a constituent element of the tape running system, the slant of the T3-post 13 must be accurately determined. However, due to small, external disturbing factors, such as a variation of tape tension Ta, a variation of friction force generated between the T3-post 13 and the tape 2, etc., the position of the upper contact point 30 unstably shifts in a direction indicated by arrow B of FIG. 9, and the position of the lower contact point 31 unstably shifts along a direction indicated by arrow C of FIG. 9. That is, the slant of the hole center line 33 with respect to the axis of the T3-arm shaft 23a is varied, and the amount and direction of slant of the T3-post 13 are unstable.
Further, in the case where tape tension Ta is not sufficiently large with respect to the weights of the T3-arm 17 and the T3-post 13, upper and lower contact points are sometimes formed at positions opposite to the upper contact point 30 and the lower contact point 31, respectively, with respect to the hole center line 33. That is, in some cases, the T3-arm shaft 23a comes in contact with the hole 17a at an upper contact point 30a and a lower contact point 31a, as shown in FIG. 9, according to the attitude of the magnetic recording/reproducing apparatus.
Furthermore, the magnitude and direction of the force applied to the T3-post 13 due to the tape tension are different between a case where the tape 2 runs in a forward direction and a case where the tape 2 runs in a reverse direction. Thus, when the running direction of the tape 2 changes between the forward and reverse directions, the positions of the upper contact point 30 and the lower contact point 31 shift, so that the amount and direction of slant of the T3-post 13 are unstable.
As described above, in the conventional structure, the amount and direction of slant of the T3-post 13 are essentially and necessarily unstable because of the attitude change or vibration of the magnetic recording/reproducing apparatus, a change in the running state of the tape 2, such as the running direction of the tape 2, the tape tension, or the like. Thus, in the conventional tape guide mechanism, the variation of the slant of the tape guidepost (T3-post 13) cannot be decreased without decreasing the space 22 shown in FIG. 7.
For example, in a practical product design, the hole 17a of the T3-arm 17 is formed at high accuracy so as to have a diameter of xcfx863.015 mmxc2x10.005 mm, and the T3-arm shaft 23a is formed so as to have an outside diameter of xcfx863 mmxc2x10.005 mm, such that the space 22 is minimized. In this case, the minimum space is 0.005 mm, and the maximum space is 0.025 mm. The variation of the slant of the T3-post 13 can be minimized by minimizing the space 22 even in the case where the upper contact point 30 and the lower contact point 31 greatly shift. However, the hole 17a and the T3-arm shaft 23a have to be formed at such a high accuracy in order to minimize the space 22.
In FIG. 8, reference mark L denotes an effective shaft length of the T3-arm shaft 23a. In a general camcorder, effective shaft length L is about 4 mm. In the case where the maximum space of 0.025 mm is obtained, the maximum slant angle xcex8 is represented by the following expression:
xcex8=tanxe2x88x921(0.025/4)=0.36xc2x0
Thus, in this case, the slant of the T3-post 13 can vary by xc2x10.36xc2x0 at a maximum only for the reason of the largeness of the space 22. As a matter of course, the variation of the slant of the T3-post 13 can be reduced by increasing effective shaft length L, but in such a case, the size of the recording/reproducing apparatus increases.
The variation of the slant of the T3-post 13 with respect to the hole 17a, which is caused in a production process, is generally about xc2x10.16xc2x0 even in a product which has met the requirement for slant in a total inspection process. The variation of a slant of the T3-arm shaft 23a with respect to the base 3, which is caused in the production process, is also generally about xc2x10.16xc2x0 even in a product which has met the requirement for slant in a total inspection process. Thus, the maximum value of the sum of these variations caused in the production process and the variation of the slant of the T3-post 13, which is caused due to the space 22, is:
(xc2x10.36xc2x0)+(xc2x10.16xc2x0)+(xc2x10.16xc2x0)=xc2x10.68xc2x0. 
Since a tape guide post of a VTR must generally be formed in an accurate fashion only with a small variation of about xc2x10.5xc2x0, each of the above tolerances cannot be increased any more. Thus, in addition to highly accurate production of each element, the total inspection must be performed solely for each element, while the total inspection must also be performed for each element in an assembled product in respect to the slant of the element.
In summary, in a conventional tape guide post mechanism, a hole of a post arm (in this conventional example, the hole 17a of the T3-arm 17) must be formed so as to have an accurate inner diameter; an arm shaft (the T3-arm shaft 23a) must be formed so as to have an accurate diameter; the slant of a tape guide post (the T3-post 13) with respect to the hole of the post arm must be accurately controlled; and the slant of the arm shaft with respect to the base (the base 3) must be accurately controlled. Accordingly, the production cost for each of these elements increases. Further, the total inspection must be performed in respect to accuracy of the slant of each element, the diameter of a hole, the diameter of a shaft, etc. As a result, the number of production steps increases, and the production cost further increases. Furthermore, the longitudinal length of the arm shaft (effective shaft length L) cannot be decreased, so that the size of the recording/reproducing apparatus cannot be decreased.
According to one aspect of the present invention, a tape guide post mechanism for guiding running of a tape includes: a post arm, the post arm including a tape guide post, around which the tape is looped, and which guides running of the tape, and a hole; an arm shaft which engages with the hole and rotatable supports the post arm, wherein the arm shaft has an elastic portion which presses a portion of the post arm.
In one embodiment of the present invention, an external surface of the arm shaft comes in contact with the hole of the post arm at two points in an upper opening of the hole and at two points in a lower opening of the hole.
In another embodiment of the present invention, the elastic portion and remainder of the arm shaft are made of different materials or parts.
According to another aspect of the present invention, a tape guide post mechanism for guiding running of a tape includes: a post arm, the post arm including a tape guide post, around which the tape is looped, and which guides running of the tape, and a hole; an arm shaft which engages with the hole and rotatably supports the post arm, wherein the post arm has an elastic portion which presses an external surface of the arm shaft.
In one embodiment of the present invention, the external surface of the arm shaft comes in contact with the hole of the post arm at two points in an upper opening of the hole and at two points in a lower opening of the hole.
In another embodiment of the present invention, the elastic portion and remainder of the post arm are made of different materials or parts.
According to the present invention, a small sized, inexpensive tape guide post mechanism, in which the slant of each element is accurately controlled, and which achieves a decrease in size of a magnetic recording/reproducing apparatus, can be obtained.
According to the present invention, an elastic portion of an arm shaft presses a portion of a post arm, whereby a constant rotational moment is caused in the post arm. Due to this constant rotational moment, variations in the amount and direction of the slant of the tape guide post can be reduced. As a result, a small sized, inexpensive tape guide post mechanism, which has a simple structure, in which the slant of each element is accurately controlled, and which achieves decreases in size and cost of the magnetic recording/reproducing apparatus, can be obtained. Furthermore, if an elastic portion is formed in the arm shaft, it is not necessary to form an elastic portion in the post arm, and therefore, the post arm can be formed in a simple structure as can be in a conventional structure.
According to the present invention, an elastic portion of a post arm presses an external surface of an arm shaft, whereby a constant rotational moment is caused in the post arm. Due to this constant rotational moment, variations in the amount and direction of the slant of the tape guide post can be reduced. As a result, a small sized, inexpensive tape guide post mechanism, which has a simple structure, in which the slant of each element is accurately controlled, and which achieves decreases in size and cost of the magnetic recording/reproducing apparatus, can be obtained. Furthermore, if an elastic portion is formed in the post arm, it is not necessary to form an elastic portion in the arm shaft, and therefore, an inexpensive, strong arm shaft can be formed from a simply structured shaft, such as a metal carved shaft or a header shaft.
According to the present invention, an arm shaft or a post arm has an elastic portion. In addition, the arm shaft comes in contact with a hole of the post arm at two contact points in an upper opening of the hole and at two contact points in a lower opening of the hole. In such a structure, the post arm is rotatable around the arm shaft, while a jolt between the arm shaft and the hole, and a variation in the relative angle between the elements, are rarely caused. As a result, a small sized, inexpensive tape guidepost mechanism, which has a simple structure, in which the slant of each element is more accurately controlled, and which achieves decreases in size and cost of the magnetic recording/reproducing apparatus, can be obtained.
Thus, the invention described herein makes possible the advantages of providing a small sized, inexpensive tape guide post mechanism for use in a magnetic recording/reproducing apparatus, which has a simple structure, in which the slant of each element is accurately controlled, and which achieves decreases in size and cost of the magnetic recording/reproducing apparatus.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.